Abstract: The change in surface morphology，functional group content，specific surface area and hydrophilicity of active carbon being modified with chemical oxidation-Fe³⁺ covering technique or HF treatment was studied with chemical analysis and surface morphology analysis. Results showed that the modified active carbon treated by chemical oxidation-Fe³⁺ covering technique has more uniform and closer pore size distribution with ordered honeycomb structure. The number of acid functional groups，specific surface area and equilibrium moisture content get increased with 0.116 meq/g，415.80 m²/g and 19.28%，respectively. Two groups of rotating biodisk (ⅠandⅡ) were prepared respectively by the above two methods and used to treat oilfield sewage for comparing the biofilm forming performance. The microbial content and biofilm dry weight of rotary-Ⅱ were measured as 2.60×10⁹ cfu/g and 16.9096 g/m²，respectively. The COD removal rates of three level biodisks were all above 80%，the highest rate reached to 92.36% under the conditions of rotary speed 4 r/min，water temperature 20^oC，HRT 6h and pH 6—8. The COD removal efficiency of biodisk-Ⅱ is better that of biodisk-Ⅰ.